A model describing the volume changes in the lung deformed by gravity and also placed in the pleural cavity has been developed. This model has been utilized to analyze excised and intact lungs undergoing various deformations, and the accuracy of the model verified by xenon clearance in anesthetized dogs. Studies relating water accumulation in isolated, perfused dog lungs to perivascular pressure have suggested that the perivascular space is first filled with fluid and then fluid enters the alveoli. Perivascular pressure seems identical to surface pressure. Studies have been performed in anesthetized normal human beings as well as awake human beings studying the effect of inspiratory flow rates on exenon clearance in various body positions. Varying the rate from .2 to 1.2 l/s had no effect on clearance. Studies have been performed in anesthetized dogs breathing spontaneously and in dogs anesthetized and paralyzed and mechanically ventilated. Differing patterns of chest deformation were quantified by magnetometers and X-rays. Despite striking differences in deformation there was no difference in regional xenon clearance. This was also verified independently by the lung deformation modeling noted above. Studies have begun on factors affecting the smooth muscle of the thoracic duct. It is found that contraction is induced by acetylcholine but that ACH receptors are not innervated. In contrast, there are alpha receptors which are innervated and cause striking contractions. Density dependence was examined in a group of individuals with chronic obstructive lung disease, and in 50% of the subjects density dependence was normal. This raises questions regarding the sensitivity of this procedure in detecting early disease. Excised lungs were studied, and based on the mathematical model, maximal expiratory flow was predicted utilizing measurements of airway diameter and compliance and lung recoil, and predictions agreed closely with the observed values. In addition, a method of exciting intact and excised lungs with white noise was developed. This has provided a description of the lung's resistance and reactance as a function of frequency. The interesting preliminary data suggests that in the dog lung at a distending pressure of 5 cm H2O, 50% of the resistance at a frequency of 5 Hz lies in airways smaller than 2mm in diameter.